1. Field of the Invention
The present invention relates to an image-capturing apparatus that controls a lens drive system during image capturing, and a driving method of an optical system.
2. Description of the Related Art
Recently, an open-loop control system using a stepping motor as an actuator has been widely used in camera drive systems. Such a control mechanism has an enhanced positioning resolution, achieving positional accuracies on the order of a few μm.
When a lens is moved with a motor in this camera drive system, a method has been known in that an operation controller detects a state of an operation member and the motor is controlled corresponding to the state and an integrated value of the state. For example, there have been provided a lever ring in that the operation member returns to the midpoint (see Japanese Unexamined Patent Application Publication No. 59-216111) and a rotary ring operation member (see Japanese Unexamined Patent Application Publication No. 63-177118). In order to have high accuracy in lens positional control and high resolution in operation, a ring has been required for controlling by such an operation controller.
On the other hand, in a lens mechanism in that a ring is mechanically connected to a lens and the lens advances or retreats in a lens barrel (mainly used for business purposes), the rotational angle of the ring is limited corresponding to the maximum advanced position or the maximum retracted position of the lens, and because the rotational angle of the ring is brought into one-to-one correspondence with the lens position, it is easy to intuitively operate this mechanism.
An example of a preexisting lens position determining method requiring the positional detection with high resolution similarly to the operation ring includes the following methods: a first is a method for obtaining an absolute position using a hall sensor and a potentiometer; a second is a method for obtaining a relative position from a reference position by combining a reset sensor with an MR (magneto resistance effect) sensor using the reset sensor for detecting the reference position and an FG (frequency generator) pulse counter (see Japanese Unexamined Patent Application Publication No. 59-216111); and a third is a method for detecting a plurality of reference positions using two or three reset sensors.